Vessels for storing ultra-cold liquefied gases must always be equipped with expensive insulation in order to keep low the level of vaporization of the liquefied gas due to heat coming in from the environment. They are consistently designed as double walled vessels whereby an insulation chamber is formed between the inner wall and the outer wall. This insulating effect is produced due to the fact that the gap between the walls is filled with a material which conducts heat poorly, for example "Superinsulation" and evacuated after the vessel is completely prepared.
Insulating vacuums of about 10.sup.-3 mbar are needed in order to reduce the heat conductivity of the gas to a minimum. Such pressures can be quickly produced by means of suitable pumping stations. Because of microleakage and desorption, the pressure would in time rise, however, after sealing the insulation chamber which would result in an increase in the rate of vaporization of the liquefied gas and a worsening of the vessel's quality. In order to prevent this from happening, adsorption materials, for example activated charcoal or molecular sieve, are installed in the chamber, namely, directly onto the inner vessel. The adsorption materials have the property of being able to adsorb a large amount of gas molecules at low temperatures, even in a vacuum, and thus insure that, under operating conditions,--in other words, with a cold inner vessel--the pressure in the insulation chamber is adequately low even after several years of the life of the vessel.
In the production of cryo-vessels, a problem is encountered, however, due to the high affinity of the adsorption agent, especially molecular sieve, for moisture. They are able to take up several percent (by weight) of water, whereby their adsorption capacity for other materials is significantly reduced. For this reason, they are activated before installation in the vessel which essentially means that they are freed from their adsorbed water. This is done by heating to 100.degree. C. (activated charcoal) or 300.degree. C. (molecular sieve) and simultaneously evacuating.
During the manufacture of the vessel, the adsorption agents are again exposed to atmospheric air so that they can again adsorb water. In addition to this, the other materials introduced into the insulation chamber are loaded with water molecules which must be removed after the construction of the vessel by heating and flushing with dry nitrogen. As a result of this, considerable partial pressures caused by water vapor can occur which likewise contribute to loading the adsorption agent with moisture again. The prior activation of the adsorption agent is, as a result, practically nullified. As a consequence of this, the heating and evacuation periods before sealing the insulation chamber are essentially lengthened thus causing an increased time expenditure as well as enormous additional energy costs.